Spatial color dithering using an active color filter and lenticular array to suppress color breakup in displays

ABSTRACT

An optical projection system that combines a lenslet array and lightvalve with an active color filter. The active color filter may be placed at either the illuminating aperture plane or at any position conjugate or incident to the output of the projection lens of the system.

FIELD OF THE INVENTION

The present invention is directed towards spatial dithering for opticalprojection displays.

BACKGROUND OF THE INVENTION

Optical projection systems in which the image is generated by lightmodulated by one or more “lightvalves” are becoming increasingly common.Devices such as televisions, presentation projectors and computermonitors have utilized such lightvalve based projection systems.Typically, in a single lightvalve system, a color image is produced byprojecting red (R), green (G) and blue (B) (collectively referred to as“primary” hereinafter) image fields in a time sequential manner withsufficient rapidity that flicker is not apparent. The overall frame ratedesired for color images is typically 60 Hertz or greater. Thus, thecorresponding interval between each color image field is {fraction(1/180)}th of a second or less.

Single lightvalve systems are relatively inexpensive and the resultingperformance is satisfactory. However, an inherent drawback of timesequential lightvalve and other systems is an effect known as ‘colorbreakup artifact’ or ‘field sequential color artifact’. Color breakupartifact manifests itself to a viewer as a transient rainbow-likefringing effect when rapid eye movements of several degrees are made.The effect is an inherent property of the human visual system butsensitivity to the effect varies greatly from person to person.Moreover, the seriousness of the effect depends strongly on the natureof the image being viewed.

One theory is that increasing the frame rate from 60 Hertz to severalhundreds or thousands of Hertz would eliminate color breakup artifact.However, since driving displays at such high frequencies presentscomplicated and expensive engineering problems, experimental evidencefor the increased frame rate theory is difficult to obtain.

An alternative approach is to abandon time sequential imaging whilestill using only one lightvalve by presenting the primary colors to theviewer in the space domain, rather than in the time domain. One way ofconstructing such a space sequential system would be to arrange the R, Gand B pixels in a mosaic pattern, like the arrangement of phosphor spotsin a Cathode Ray Tube device. The lightvalve would be illuminated usingwhite light, and each R pixel would be covered with a red filter, each Gpixel with a green filter and each B pixel with a blue filter. Therequisite filter array would contain about 10⁶ or more filters.Furthermore, in the case of a micro-display lightvalve array, eachfilter would measure only 10×10 μm². Though conceptually easy,implementing such large filter arrays and such small individual filterscould be prohibitively expensive. Disadvantageously, compared to fieldsequential imaging, mosaic filter arrays need about three times as manypixels.

An approach which does not suffer from the disadvantage of an increasedpixel count has also been proposed. Though using a mosaic filter, thefilter is ‘spatially dithered’ over the lightvalve by approximately plusor minus one pixel horizontally and vertically. For a 60 Hertz framerate, the ‘dither rate’ would be about 180 Hertz. A conventional way toachieve dithering is in the use of a spatial multiplexer. A possibledisadvantage of the spatial multiplexer is the cost of the deviceitself. Another is its thickness of 3 to 5 millimeters, which wouldincrease the back focal length required of the projection lens, therebyincreasing the cost of the projection optics. A third is that it entailsthe use of a mosaic filter.

Thus there is a need to implement spatial dithering with a lower costand complexity.

SUMMARY

The invention in one or more embodiments consists of lenslet arrayplaced immediately in front of a lightvalve, and a segmented activecolor filter placed at the projection lens' aperture stop or at anyposition optically conjugate thereto. Using a segmented color filterthat is ‘active’ (in the sense that the colors of the filter segmentsare sequenced), the spatial dithering process can be placed underelectronic control. In various embodiments, the active color filter canproduce any pattern and configuration of colors, which are then repeatedthroughout the lightvalve. Further, in some embodiments, the lensletarray and lightvalve may be separated from one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic of an exemplary optical system employingone or more embodiments of the invention involving spatial dithering viaa lenticular array.

FIG. 2 illustrates a portion of the lightvalve of FIG. 1 and depicts thethree phases of the active color filter.

FIG. 3 illustrates an projection system utilizing an active color filterand lenticular array according to one or more embodiments of theinvention.

FIG. 4 illustrates nine different color pixels as they would appear onan imaging screen.

FIG. 5 illustrates a portion of a lightvalve generated by a four pixelblock active color filter using Red, Green and Blue.

FIG. 6 illustrates a portion of a lightvalve generated by a four pixelblock active color filter using Red, Green, Blue and White.

FIG. 7 illustrates a portion of a lightvalve generated by a stripedpattern active color filter.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed toward implementing spatial dithering in anovel manner. One or more embodiments described herein places alenticular array just in front of the lightvalve, and a segmented activecolor filter at a position incident to or optically conjugate to theprojection lens' aperture stop. Using a segmented color filter that is‘active’ (in the sense that the colors of the filter segments aresequenced), the spatial dithering process can be placed under electroniccontrol. Color sequencer devices, which are readily available, may beused to sequence or change the colors of the filter.

FIG. 1 illustrates a schematic of an exemplary optical system employingone or more embodiments of the invention. The optical system consists ofa lightvalve 110 built upon a lenticular array 120 as well as a filter170. Filter 170 is shown sectioned in three and is an active orelectronically controlled filter which can sequence colors. The opticalsystem illustrated in FIG. 1 is configured to provide spatial ditheringvia a lenticular array 120 and performs two vital functions:

1) The system maps each pixel of a lightvalve 110 into a correspondinglocation of a virtual image plane IP2; and

2) The system maps a given number of k sections of the active colorfilter 170 onto each group of k pixels of the image onto screen 190.

For the purposes of illustration, the field lens 130 and projection lens140 are assumed to be thin and ideal. A portion of the lightvalve 110shown in FIG. 1 is a vertical section through the ‘a’ column of thearray. The optical system of FIG. 1 is assumed to have the filter 170operating in one of its phases (sequence and arrangement of colors). Theoptical system of FIG. 1 has the following characteristics andparameters:

The focal length of the lenticules (of any section of the lenticulararray 120) into glass is f₁;

The focal length of the lenticules (of any section of the lenticulararray 120) into air is f₂.

Thus, if the glass has a refractive index of N, and the radius ofcurvature of each lenticule is R, then:$\frac{N}{f_{1}} = {\frac{1}{f_{2}} = \frac{N - 1}{R}}$

The active color filter 170 is placed at the plane of the projectionlens 140. (In the case of a thick projection lens, it would be placedapproximately at its principal plane.)

The focal length of the field lens 130 is F, and the separation betweenthe field lens 130 and prrojection lens 140 is equal to F

The plane IP1 (coincident with the plane of screen 190 upon which theimage is displayed) is conjugate to the plane of the field lens 130.

The rays emanating from pixels a1, a2 and a3 are assumed to be parallelto the optic axis. The rays emanating from a1, a2 and a3 are brought toa common image point A1-3 in image plane IP1 (screen 190). In thesection shown, all the rays from a3 pass through the region between S1to S2 in the plane of the projection lens 140. This corresponds to afirst section (labeled section 1) of the active color filter 170.Similarly, the rays emanating from a2 pass through the region between S2and S3 in the plane of the projection lens 140 corresponding to a secondsection (labeled section 4) of the active color filter 170. The raysemanating from a3 pass through the region between S3 and S4 in the planeof the projection lens 140, corresponding to the third section (labeledsection 7) of the active color filter 170.

Similar rays (i.e. rays parallel to the optic axis) emanating frompixels a4, a5 and a6 are not depicted in FIG. 1, but given the opticalcharacteristics of the system, these rays are brought to a common imagepoint at A4-6 in plane IP1 (screen 190). All the rays emanating from a4pass through section 7 of the active color filter 170, those from a5pass through Section 4 and those from a6 pass through section 1.

By induction, in general:

All rays emanating parallel to the optic axis from any group of threepixels served by the same lenticule are brought to a common image pointat the plane IP1 (screen 190).

All the rays emanating parallel to the optic axis from pixels such asa1, a4, a7, . . . a(1+3n), where n is an integer, pass through Section 7of the active color filter 170.

All the rays emanating parallel to the optic axis from pixels such asa2, a5, a8, . . . a(2+3n), where n is an integer, pass through Section 4of the active color filter 170.

All the rays emanating parallel to the optic axis from pixels such asa3, a6, a9, . . . a(3+3n), where n is an integer, pass through Section 1of the active color filter 170.

While FIG. 1 has been drawn as an approximation and is not to scale, theoptical elements therein behave with the following properties:

1) The distance (D1) between the image point in plane IP1 (screen 190)and the optic axis is proportional to the distance (D2) between thecentral pixel in the group of three and the optic axis in the plane ofthe lightvalve 110; and

2) The constant of proportionality between distances D1 and D2 is equalto the magnification of the projection lens 140.

The rays emanating from a13 to a15 are shown as emitted into a cone fromthe center of each pixel. These rays will from a superimposed patch atA13-15 in image plane IP1. The plane of the active color filter 170 isconjugate with the plane of the lightvalve 110. As a result, all therays from pixel a15 are imaged at the center of section 1 of the activecolor filter 170. All the rays from a14 are imaged at the center ofsection 4 of the active color filter 170 and all the rays from a13 areimaged at the center of section 7 of the active color filter 170.

Given the above optical constraints, similar rays (i.e. rays from thecenter of each pixel) emanating from pixels a10, a11 and a12 (notdepicted in FIG. 1), are brought to a common superimposed patch atA10-12 in plane IP1 (screen 190). Likewise, all the rays from a12 passthrough section 1 of the active color filter 170, those from all passthrough section 4 of the active color filter 170 and those from a10 passthrough section 7 of the active color filter 170.

In general:

All rays emanating from the center of each pixel in a group of threepixels served by the same lenticule are brought to a common superimposedpatch at the plane IP1 (screen 190).

All the rays emitted from the centers of pixels a1, a4, a7, . . .a(1+3n), where n is an integer, pass through the center of section 7 ofthe active color filter 170.

All the rays emitted from the centers of pixels a2, a5, a8, . . .a(2+3n) pass through the center of section 4 of the active color filter170.

All the rays emitted from the centers of pixels a2, a5, a8, . . .a(2+3n) pass through the center of section 1 of the active color filter170.

Furthermore, the following properties apply to the optics depicted inFIG. 1:

1) The distance (D3) between the center of the patch in image plane IP1(screen 190) and the optic axis is proportional to the distance (D4)between the central pixel in the group of three and the optic axis inthe plane of the lightvalve 110; and

2) The constant of proportionality between distances D3 and D4 is equalto the magnification of the projection lens 140.

For illustration, assume that a white area is being imaged. Then regionssuch as A13-15, A10-12, A7-9, A4-6, and A1-3 will be colored white, andthe regions between them will (to first order) not be illuminated. Sincepatch A13-15 represents a combination of pixels a13, a14 and a15, and soon, this means that each group of 3 pixels (not the individual pixelsthemselves) of the lightvalve 110 is represented at the screen 190.

In one embodiment of the invention, the projected image may be viewed atan image plane such as IP1 (screen 190). Image plane IP1 is offset fromimage plane IP2, and is chosen such that the patches A15, A14 and A13and A3, A2 and A1 are individually resolved on the screen 190. Sincepatch A14 corresponds to pixel a14, and so on, this means that theindividual pixels of the lightvalve 110 are mapped on to the plane IP2.Furthermore, the optical system has the desired effect of mapping theactive color filter 170 ‘in parallel’ onto each group of pixels servedby a given lenticule.

The image plane IP2 represents a plane at which there is no gap oroverlap between the projected image pixels. Assume that L is the imagedistance of the projection lens 140 (i.e. the distance between the imageplane IP2 and the projection lens 140). Assume also that P representsthe dimension of a pixel at the screen 190 (e.g. the distance betweenpixels such as A1 and A2) and that S is the linear dimension of eachsection of the active color filter 170. It can be shown by geometricproof that the offset distance, Δ, between image planes IP1 and IP2 isgiven by: $\Delta = \frac{P*L}{S}$

FIG. 2 illustrates a portion of the lightvalve 110 of FIG. 1 and depictsthe three phases of the active color filter. The lightvalve 110 used inthe optics system of FIG. 1 shows only the ‘a’ column of the lightvalve200 depicted in FIG. 2. Looking into the plane of FIG. 1, the lightvalvetherein would have at least as many columns such as ‘a’ through ‘n’depicted in FIG. 2. The lightvalve is modulated by an active colorfilter which operates in three phases. Each phase should last for{fraction (1/180)} second if the image frame rate is to be 60 Hertz.

The optical projection system in various embodiments of the inventionmaps the nine sections of the active color filter onto each group ofnine pixels of the lightvalve 200 (or equivalently, of the image). As aresult of the mapping, the following occurs:

1) The color of each pixel in the projected image is determined by atime sequential process. (A time interval of {fraction (1/180)} secondis available for each of the primary colors at a 60 Hertz frame rate.)

2) At any given time, approximately ⅓ of the pixels in the projectedimage are red, ⅓ are green and ⅓ are blue when a white area is beingdisplayed.

For instance, in a 60 Hertz desired frame rate, each section of thefilter will exist in a R (Red) state for {fraction (1/180)} second, inthe G (Green) state for {fraction (1/180)} second and in the B (Blue)state for {fraction (1/180)} of a second. This varying color projectionsuppresses the color breakup artifact effect in the image.

The nine-pixel block 210 is what the active color filter produces duringphase 1 of its operation. The lightvalve 200 is shown in its state whenthe active color filter operates in phase 1 and thus repeats block 210starting from pixel location a1. For instance, in row 1, pixel a1 showsa Red colored intensity, pixel b1 shows a Blue colored intensity andpixel c1 shows a Green intensity. Pixels a2, b2 and c2 of row 2 showGreen, Red and Blue, respectively, and pixels a3, b3 and c3 of row 3show Blue, Green and Red, respectively. Though not shown on lightvalve200, the nine-pixel block 220, which is produced by the active colorfilter operating in phase 2, would be repeated throughout lightvalve 200starting at pixel location a1. Likewise, the nine-pixel block 230, whichis produced by the active color filter operating in phase 3, would berepeated throughout lightvalve 200 tarting at pixel location a1.

The overall effect of sequencing the filter through these phases is acombination of Red, Green and Blue intensities for each pixel locationin the lightvalve 200. Thus, all the pixel locations a1, a2, a3, . . . ,all, b1, b2, b3, . . . , b11 . . . n1, n2, n3, . . . n11 will show acombination of Red, Green and Blue within {fraction (1/60)}th of asecond, giving a frame rate of 60 Hertz. Red, Green and Blue are evenlyrepresented in each of the three filter phases which may reduceflickering.

FIG. 3 illustrates a projection system 300 utilizing an active colorfilter and lenticular array according to one or more embodiments of theinvention. The projection system 300 is initiated by a lamp 310 which istypically a spatially confined light source with a reflector. The lightsupplied by lamp 310 is shone into an optical integrator 320. Opticalintegrator 320 is a slab of glass, typically rectangular inconfiguration, which by internally reflecting causes the light from lamp310 to become spatially uniform. The output of the optical integrator320 is a set of light rays that will eventually be imaged onto alightvalve & lenslet array assembly 360. For this purpose, theprojection system 300 uses telecentric relay 330 composed of a series ofconcentrating lenses which focus the light from optical integrator 320onto the appropriate portions of the lightvalve & lenslet array assembly360. The lenslet array portion of lightvalve & lenslet array assembly360 is lenticular in configuration (as shown in FIG. 1) for aone-dimensional dithering, and rectangular for a two-dimensionaldithering.

In an embodiment of the invention, an active color filter 340 is placedat an illuminating aperture plane 335 (between the lens structurehalves) of the telecentric relay 330. Active color filter 340 is anactive color filter with Red, Green and Blue sections, for example, andpreferably, is switchable electronically. Using an electronicallyswitchable filter for the active color filter 340 enables it to providetime sequential or phased output. As discussed above with regard to FIG.2, the active color filter can be programmed to cycle fully throughthree phases with each phase duration being {fraction (1/180)}th of asecond (thus, achieving a 60 Hertz overall frame rate).

The active color filter 340 is placed such that the illuminatingaperture plane 335 coincides with the output plane of the active colorfilter 340. The optical projection system is configured such that theilluminating aperture plane 335 and the imaging aperture plane 375 areoptically ‘conjugate’ to one another. As a result of being opticallyconjugate, any point in the illuminating aperture plane 335 is imagedonto a corresponding point in the imaging aperture plane 375.Advantageously, and unlike other systems, since the planes 335 and 375are optically conjugate, the active color filter 340 may be placed atthe illuminating aperture plane 335 instead of the imaging apertureplane 375 (as shown in the FIG. 1 system). This may be of considerablepractical advantage since the illuminating aperture plane 335 is usuallymore accessible than the imaging aperture plane 375.

The lightvalve & lenslet array assembly 360 is placed behind apolarizing beamsplitter 350. The polarizing beamsplitter 350 performsthe function of separating the illuminating light coming from thetelecentric relay 330 from the light reflected by the lightvalveassembly 360. The lightvalve changes the polarization of light which isto form the image. Hence, due to reflection from the hypotenuse 355 ofthe polarizing beamsplitter 350, the light which is to form the image isdirected through a projection lens 370. The polarizing beamsplitter 350thus diverts the image through the projection lens 370.

Projection lens 370 is a sequence of lensing elements projecting theoutput of the lightvalve & lenslet array assembly 360 onto the viewingscreen (not shown). Due to the arrangement of the elements of theprojection system 300, the illuminating aperture plane 335 and imagingaperture plane 375 are conjugate to one another in the optical sense,this allows the active color filter 340 to be placed at the illuminatingaperture plane 335 which may have commercial/practical implementationadvantage. In other embodiments, for example, the lenslet array andlightvalve can be built and placed separate from one another. Where thelenslet array and lightvalve are separated from one another, the relayoptics may have a different role. For instance, if the lenslet arraywere placed between the filter and the relaying optics, the relayingoptics would have to resolve single pixels. A variety of arrangements ofthe integrator, lenslet arrays and filters may be possible dependingupon preference or design.

FIG. 4 illustrates nine image pixels, each of a different color, as theywould be viewed on a screen placed at the plane IP2. This particulargroup of pixels extends from A1 to C3. These different image colors canbe achieved by driving each of the corresponding lightvalve pixelsappropriately during its three phases. The combined effect of thesedrives, listed in FIG. 4 and in the table below, is a full frame pixelof the appropriate color. The nine pixel section lightvalve shown inFIG. 2, in phases 1, 2 and 3, is used to arrive at the following drives,shown on a relative basis, from a minimum of zero to a maximum of one:

Phase Phase Phase Pixel Color 1 2 3 Al Black 0 0 0 Bi Red 0 1 0 C1 Green1 0 0 A2 Blue 0 1 0 B2 Yellow 1 1 0 C2 Cyan 1 0 1 A3 Magenta 1 1 0 B3White 1 1 1 C3 50% ½ ½ ½ Gray

By way of illustration, consider pixel A3 on the screen which is to beimaged as a Magenta colored full frame pixel. From FIG. 2, the pixel a3on the lightvalve corresponds to Section 7 of the active color filter.For this section, Blue (B) is transmitted during phase 1, Red (R) istransmitted during phase 2 and Green (G) during phase 3. From the tableabove, the drive voltages for the pixel A3 are 1 during phases 1 and 2,and 0 during phase 3. Therefore, the screen will, over the course of acomplete frame, be illuminated with relative intensities of 1 of Blue(corresponding to phase 1), 1 of Red (corresponding to phase 2) and 0 ornone of Green (corresponding to the drive on phase 3). When viewedtogether this combination of drive voltages when applied will protect amagenta color for pixel position A3. Black pixels are absent of Red,Green and Blue and thus, are not driven (have zero drive voltagesapplied to them) during the three phases.

Though only nine different color pixels are shown, a total of 27 colorsmay be represented given possible drive voltages of only 0, ½, and 1. Byfurther discriminating the available level of drive voltages that may beapplied to the three phases, the richness of color variation can beincreased. For instance, the drive voltages may be differentiated inincrements of ¼ rather than ½. This would yield five (5) levels of drivevoltages, 0, ¼, ½, ¾ and 1 and yields 125 different colors. In general,given that there are k drive levels for a three phase active colorfilter (or switchable filter), then the total available colors arek{circumflex over ( )}3.

FIG. 5 illustrates a section of a lightvalve generated by a four pixelblock active color filter using Red, Green and Blue. In FIG. 2, a ninepixel block sequencer produces the pattern through the lightvalve. Thenumber and arrangement of the pixels in the active color filter islargely a matter of preference and will appear in the same pattern overthe pixel locations of the lightvalve. A four-pixel block 510 is shownas a result of an active color filter operating in Phase 1. The activecolor filter in Phase 1 of its operation produces a pattern of a Redpixel in the upper left and lower right, a Green pixel in the upperright and a Blue pixel in the lower left of the block 510. Thelightvalve 500 is shown to mirror this pattern. On the lightvalve 500,pixel a1 and b2 show Red while pixel a2 shows Blue and pixel b1 showsGreen. This arrangement is repeated with pixels c1, d1, c2 and d2, whichforms a block to the right of the block formed by pixels a1, a2, b1 andb2. Likewise, an identical four-pixel block starts below pixel a2 atpixel a3, and covers pixels a3, a4, b3 and b4. The pattern of two Redcolored pixel locations and one Green and one Blue appears as a resultof the active color filter being in Phase 1 of its operation which lastsfor {fraction (1/180)}th of a second (in the case of a desired overallframe rate of 60 Hertz).

In Phase 2 of its operation, a four-pixel block 520 with two Greenpixels, one Blue pixel, and one Red pixel are generated by the activecolor filter. The Green pixels are located in the upper left and lowerright of block 520 while the Red pixel is located lower left of block520 and the Blue pixel in the upper right of block 520. While not shown,lightvalve 500 will repeatedly display the pattern of block 520 startingfrom pixel location al when the active color filter operates in Phase 2.

In Phase 3 of its operation, a four-pixel block 530 with two Bluepixels, one Green pixel, and one Red pixel are generated by the activecolor filter. The Blue pixels are located in the upper left and lowerright of block 520 while the Red pixel is located lower left of block520 and the Green pixel in the upper right of block 520. While notshown, lightvalve 500 will repeatedly display the pattern of block 530starting from pixel location al when the active color filter operates inPhase 3.

The combined effect of applying Phase 1, 2 and 3 filtering of the activecolor filter through lightvalve 500 is a combination of Red, Green andBlue intensities for each pixel location. Thus, all the pixel locationsa1, a2, a3, . . . , a11, b1, b2, b3, . . . , b11 . . . n1, n2, n3, . . .n11 will show a combination of Red, Green and Blue within {fraction(1/60)}th of a second, giving a frame rate of 60 Hertz. In Phase 1,there is a predominance of Red pixels, in Phase 2, a predominance ofGreen pixels and in Phase 3, a predominance of Blue pixels.

FIG. 6 illustrates a lightvalve generated by a four pixel block activecolor filter using Red, Green, Blue and White. A four-pixel block 610 isshown as a result of an active color filter operating in Phase 1. Theactive color filter in Phase 1 of its operation produces a pattern of aRed pixel in the upper left, a Green pixel in the upper right, a Bluepixel in the lower left and a White pixel in the lower right of theblock 610. The lightvalve 600 is shown as mirroring this pattern. On thelightvalve 600, pixel al shows Red while pixel a2 shows Blue, pixel b1shows Green and pixel b2 shows White. This arrangement is repeated withpixels c1, d1, c2 and d2, which forms a block to the right of the blockformed by pixels a1, a2, b1 and b2. Likewise, an identical for pixelblock starts below pixel a2 at pixel a3, and covers pixels a3, a4, b3and b4. The pattern of one Red colored pixel location, one Green, oneBlue and White appears as a result of the color sequencer being in anyone phase of its operation which lasts for {fraction (1/180)}th of asecond (in the case of a desired overall frame rate of 60 Hertz).

In Phase 2 of its operation, a four-pixel block 620 with the same oneGreen pixel, one Blue pixel, one Red pixels and one White pixel aregenerated by the color sequencer, but in a different orientation fromblock 610. The Green pixel is located in the upper left of block 620while the Red pixel is located lower right of block 620 the Blue pixelan the upper right of block 620 and the White pixel in the lower left ofblock 620. While not shown, lightvalve 600 will repeatedly display thepattern of block 620 starting from pixel location a1 when the colorsequencer operates in Phase 2.

In Phase 3 of its operation, a four-pixel block 620 with the same oneGreen pixel, one Blue pixel, one Red pixels and one White pixel aregenerated by the active color filter, but in a different orientationfrom block 610 or 620. The Blue pixel is located in the upper left ofblock 630 while the Green pixel is located lower right of block 630 theWhite pixel in the upper right of block 630 and the Red pixel in thelower left of block 630. While not shown, lightvalve 600 will repeatedlydisplay the pattern of block 630 starting from pixel location a1 whenthe active color filter operates in Phase 3.

The combined effect of applying Phase 1, 2 and 3 filtering of the activecolor filter through lightvalve 600 is a combination of Red, Green, Blueand White intensities for each pixel location. Thus, all the pixellocations a1, a2, a3, . . . , a11, b1, b2, b3, . . . , b11 . . . n1, n2,n3, . . . n11 will show a combination of Red, Green, Blue and Whitewithin {fraction (1/60)}th of a second, giving a frame rate of 60 Hertz.Unlike the lightvalve pattern produced at each in the FIG. 5 example, nosingle color, Red, Green, Blue nor White predominates at a given phase.Further, with the addition of a White filtered pixel, the total imageproduced can exhibit a 50% greater luminance over the lightvalves shownin FIGS. 2 and 5 when displaying pixels whose composite color over thethree phases is to be White. However, this also implies that theluminances when displaying the colors Red, Green and Blue, in composite,would be 25% less (due to the ¼ fewer pixels transmitted in each primarycolor).

FIG. 7 illustrates a lightvalve generated by a striped pattern activecolor filter. Striped pixel block 710 results from the active colorfilter operating in Phase 1. Block 710 exhibits a first row of Redpixels followed by a row of Green pixels and then a row of Blue pixels.This striped pattern is repeated every three rows of lightvalve 700 whenthe active color filter supplies Phase 1 filtered light rays.

Striped pixel block 720 results from the active color filter operatingin Phase 2. Block 720 exhibits a first row of Green pixels followed by arow of Blue pixels and then a row of Red pixels. While not shown,lightvalve 700 will repeatedly display the striped pattern of block 720starting from pixel row “a” when the active color filter operates inPhase 2. Striped pixel block 730 results from the active color filter inPhase 1. Block 730 exhibits a first row of Blue pixels followed by a rowof Red pixels and then a row of Green pixels. While not shown,lightvalve 700 will repeatedly display the striped pattern of block 730starting from pixel row “a” when the active color filter operates inPhase 3. The lenticular array for such a striped pattern would be madecylindrical with a width equivalent to 3 lightvalve pixels. The combinedeffect of applying Phase 1, 2 and 3 filtering of the active color filterthrough lightvalve 700 is a combination of Red, Green, and Blueintensities for each pixel location of lightvalve 700. Thus, all thepixel locations a1, a2, a3, . . . , a11, b1, b2, b3, . . . , b11 . . .n1, n2, n3, . . . n11 will show a combination of Red, Green, Blue andWhite within {fraction (1/60)}th of a second, giving a frame rate of 60Hertz.

While the invention has been described with reference to numerousspecific details, one of ordinary skill in the art will recognize thatthe invention can be embodied in other specific forms without departingfrom the spirit of he invention. Thus, one of ordinary skill in the artwill understand that the invention is not to be limited by the foregoingillustrative details, but rather is to be defined by the appendedclaims.

We claim:
 1. A system for optical projection of light rays from aprojection lens through a lightvalve, said system comprising: a lensletarray placed immediately in front of said lightvalve; an active colorfilter placed about the system such that said filter is opticallyconjugate with the aperture stop of said projection lens.
 2. A systemaccording to claim 1 wherein said active color filter array is segmentedinto a pattern of pixel locations.
 3. A system according to claim 2wherein said active color filter operates in a sequence of phases, eachphase producing a component of the total image color at a particularpixel location.
 4. A system according to claim 3 wherein the number ofphases comprising the sequence is three.
 5. A system according to claim1 wherein said lenslet array and said lenslet array are integrated intoone assembly.
 6. A system according to claim 4 wherein said active colorfilter produces Red, Green and Blue intensity components.
 7. A systemaccording to claim 6 further wherein said active color filter produces aWhite intensity component.
 8. A system according to claim 6 wherein saidpattern consists of three rows and three columns of pixel locationsgiving a total of nine segments.
 9. A system according to claim 6wherein said pattern consists of two rows and two columns of pixellocations giving a total of four segments.
 10. A system according toclaim 7 wherein said pattern consists of two rows and two columns ofpixel locations giving a total of four segments.
 11. A system accordingto claim 8 wherein the active color filter operating in the first ofsaid three phases generates: a first row of said three rows of pixellocations, said first row patterned to have the first column locationRed, the second column location Blue and the third column locationGreen; a second row of said three rows of pixel locations, said secondrow patterned to have the first column location Green, the second columnlocation Red and the third column location Blue; and a third row of saidthree rows of pixel locations, said third row patterned to have thefirst column location Blue, the second column location Green and thethird column location Red.
 12. A system according to claim 11 whereinthe active color filter operating in the second of said three phasesgenerates: a first row of said three rows of pixel locations, said firstrow patterned to have the first column location Green, the second columnlocation Red and the third column location Blue; a second row of saidthree rows of pixel locations, said second row patterned to have thefirst column location Blue, the second column location Green and thethird column location Red; and a third row of said three rows of pixellocations, said third row patterned to have the first column locationRed, the second column location Blue and the third column locationGreen.
 13. A system according to claim 12 wherein the active colorfilter operating in the third of said three phases generates: a firstrow of said three rows of pixel locations, said first row patterned tohave the first column location Blue, the second column location Greenand the third column location Red; a second row of said three rows ofpixel locations, said second row patterned to have the first columnlocation Red, the second column location Blue and the third columnlocation Green; and a third row of said three rows of pixel locations,said third row patterned to have the first column location Green, thesecond column location Red and the third column location Blue.
 14. Asystem according to claim 9 wherein the active color filter operating inthe first of said three phases generates: a first row of said two rowsof pixel locations, said first row patterned to have the first columnlocation Red and the second column location Green; and a second row ofsaid two rows of pixel locations, said second row patterned to have thefirst column location Blue and the second column location Red.
 15. Asystem according to claim 14 wherein the active color filter operatingin the second of said three phases generates: a first row of said tworows of pixel locations, said first row patterned to have the firstcolumn location Green and the second column location Blue; and a secondrow of said two rows of pixel locations, said second row patterned tohave the first column location Red and the second column location Green.16. A system according to claim 15 wherein the active color filteroperating in the third of said three phases generates: a first row ofsaid two rows of pixel locations, said first row patterned to have thefirst column location Green and the second column location Blue; and asecond row of said two rows of pixel locations, said second rowpatterned to have the first column location Red and the second columnlocation Green.
 17. A system according to claim 10 wherein the activecolor filter operating in the first of said three phases generates: afirst row of said two rows of pixel locations, said first row patternedto have the first column location Red and the second column locationGreen; and a second row of said two rows of pixel locations, said secondrow patterned to have the first column location Blue and the secondcolumn location White.
 18. A system according to claim 17 wherein theactive color filter operating in the second of said three phasesgenerates: a first row of said two rows of pixel locations, said firstrow patterned to have the first column location Green and the secondcolumn location Blue; and a second row of said two rows of pixellocations, said second row patterned to have the first column locationWhite and the second column location Red.
 19. A system according toclaim 18 wherein the active color filter operating in the third of saidthree phases generates: a first row of said two rows of pixel locations,said first row patterned to have the first column location Blue and thesecond column location White; and a second row of said two rows of pixellocations, said second row patterned to have the first column locationRed and the second column location Green.
 20. A system according toclaim 6 wherein said pattern consists of three rows pixel locationsgiving a total of three striped segments.
 21. A system according toclaim 20 wherein the active color filter operating in the first of saidthree phases generates: a first row of said three rows of pixellocations, said first row patterned to have all column locations Red; asecond row of said three rows of pixel locations, said second rowpatterned to have all column locations Green; and a third row of saidthree rows of pixel locations, said third row patterned to have allcolumn locations Blue.
 22. A system according to claim 21 wherein theactive color filter operating in the second of said three phasesgenerates: a first row of said three rows of pixel locations, said firstrow patterned to have all column locations Green; a second row of saidthree rows of pixel locations, said second row patterned to have allcolumn locations Blue; and a third row of said three rows of pixellocations, said third row patterned to have all column locations red.23. A system according to claim 22 wherein the active color filteroperating in the third of said three phases generates: a first row ofsaid three rows of pixel locations, said first row patterned to have allcolumn locations Blue; a second row of said three rows of pixellocations, said second row patterned to have all column locations Red;and a third row of said three rows of pixel locations, said third rowpatterned to have all column locations Green.
 24. A system according toclaim 1 further comprising: a polarizing beamsplitter having ahypotenuse that enables said beamsplitter to behave as a plane mirror,said beamsplitter positioned betwixt said active color filter and saidlenslet array.
 25. A system according to claim 1 further comprising: alamp which acts as initial source of light for said system; and anoptical integrator focusing rays generated by said lamp into said activecolor filter.
 26. A system according to claim 1 wherein said activecolor filter is incident with the plane of said projection lens.
 27. Asystem according to claim 25 further comprising a telecentric relayplaced between said optical integrator and said lightvalve, saidtelecentric relay illuminating said lightvalve and having anilluminating aperture plane.
 28. A system according to claim 27 whereinsaid active color filter is incident with said illuminating apertureplane.
 29. A system for optical projection of light rays from aprojection lens through a lightvalve, said system comprising: a lensletarray separated from said lightvalve; an active color filter placedabout the system such that said filter is optically conjugate with theaperture stop of said projection lens.